1.Ball valve structure
The ball valve is evolved from the plug valve. Its opening and closing parts are used as a sphere, and the sphere is rotated 90 degrees around the axis of the valve stem to achieve the purpose of opening and closing.The ball valve is mainly used to cut off, distribute and change the flow direction of the medium on the pipeline. The ball valve designed with V-shaped opening also has a good flow adjustment function. The ball valve is not only simple in structure and good in sealing performance, but also small in volume, light in weight, low in material consumption, small in installation size, small in driving torque, easy to operate and easy to open and close quickly within a certain nominal diameter range. One of the fastest growing valve varieties in more than ten years. Especially in developed industrial countries such as the United States, Japan, Germany, France, Italy, Spain, and the United Kingdom, the use of ball valves is very extensive, and the variety and quantity of ball valves are still expanding. Its reliability and other performance indicators have reached a high level, and it has partially replaced gate valves, globe valves and regulating valves.
2.Ball valve Feature
- Has the lowest flow resistance (practically zero).
- It can be used reliably in aggressive media and low-boiling liquids because it does not stick during operation (without lubricant).
- Complete sealing can be achieved in a wide range of pressure and temperature.
- Ball closures are automatically positioned in position.
- The working medium is reliably sealed on both sides.
- When fully open and fully closed, the sealing surfaces of the ball and valve seat are isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface.
- With compact structure and light weight, it can be considered as the most reasonable valve structure for low temperature medium system.
- The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline.
- The closure can withstand high pressure differentials when closed.
- The ball valve with fully welded valve body can be directly buried in the ground, so that the valve internals are not corroded, and the maximum service life can reach 30 years. It is the most ideal valve for oil and natural gas pipelines.
Because the ball valve has the above advantages, it has a wide range of applications, and the ball valve can be applied to:
- Nominal pass from 8mm to 1200mm.
- Nominal pressure from vacuum to 42MPa.
- The working temperature is from -204℃~815℃.
3.Ball valve Sealing Ability
The most important seat sealing ring material of ball valve is polytetrafluoroethylene (PTFE), which is inert to almost all chemical substances, and has a small friction coefficient, stable performance, not easy to age, wide temperature range and excellent sealing performance. comprehensive characteristics. But the physical properties of PTFE, including high coefficient of expansion, susceptibility to cold flow, and poor thermal conductivity, require that seat seal designs must be built around these properties. Plastic materials for seat seals also include filled PTFE, nylon, and many others. However, when the sealing material hardens, the reliability of the sealing is compromised, especially under the condition of low pressure drop. In addition, synthetic rubber such as nitrile rubber can also be used as a valve seat sealing material, but its applicable medium and temperature range are limited. In addition, if the medium is not lubricated, the use of synthetic rubber tends to trap the ball.
In order to meet the application requirements of high temperature, high pressure, strong erosion, long life and other industrial applications, the metal sealing ball valve has been greatly developed in the past ten years. Especially in industrially developed countries, such as the United States, Italy, Germany, Spain, the Netherlands, etc., the structure of the ball valve has been continuously improved, and the fully welded valve body directly buried ball valve, lifting ball valve, and the ball valve are used in long-distance pipelines, oil refining equipment, etc. The application in the industrial field is becoming more and more extensive, and there are ball valves with large diameter (3050mm), high pressure (70MPa) and wide temperature range (-196~815℃), so that the technology of ball valves has reached a new level.
3.Ball valve Applications
Since the ball valve usually uses rubber, nylon and polytetrafluoroethylene as the material of the seat seal, its operating temperature is limited by the material of the seat seal. The cut-off function of the ball valve is accomplished by pressing the metal ball against the plastic valve seat under the action of the medium (floating ball valve). Under the action of a certain contact pressure, the valve seat sealing ring undergoes elastic-plastic deformation in local areas. This deformation can compensate for the manufacturing accuracy and surface roughness of the sphere and ensure the sealing performance of the ball valve.
And because the valve seat sealing ring of the ball valve is usually made of plastic, when choosing the structure and performance of the ball valve, the fire resistance and fire resistance of the ball valve should be considered, especially in the petroleum, chemical, metallurgical and other departments, in flammable and explosive media. If ball valves are used in the equipment and pipeline systems, more attention should be paid to fire resistance and fire protection.
Usually, in two-position adjustment, strict sealing performance, mud, wear, shrinking channel, quick opening and closing (1/4 turn opening and closing), high pressure cut-off (large pressure difference), low noise, cavitation and gasification, Ball valves are recommended for pipeline systems with small amount of leakage to the atmosphere, small operating torque and small fluid resistance.
Ball valves are also suitable for pipeline systems with light structure, low-pressure cut-off (small pressure difference), and corrosive media.Ball valves can also be used in cryogenic (cryogenic) installations and piping systems.In the oxygen pipeline system in the metallurgical industry, ball valves that have undergone strict degreasing treatment are required. When the main lines in oil pipelines and gas pipelines need to be buried underground, full-bore welded ball valves are required.When the adjustment performance is required, a ball valve with a special structure with a V-shaped opening should be selected.In petroleum, petrochemical, chemical, electric power, and urban construction, metal-to-metal sealing ball valves can be used in pipeline systems with operating temperatures above 200 °C.
3.Ball valve Selection Tips
- Oil and natural gas transmission main lines, pipelines that need to be cleaned, and buried in the ground, choose a ball valve with a full-pass and full-welded structure; buried in the ground, choose a ball valve with a full-pass welded connection or flange connection; branch pipes, choose flange connection, welded connection, full through or reduced diameter ball valve.
- The pipelines and storage equipment of refined oil use flanged ball valves.
- On the pipeline of city gas and natural gas, the floating ball valve with flange connection and internal thread connection is selected.
- In the oxygen pipeline system in the metallurgical system, it is advisable to use a fixed ball valve that has undergone strict degreasing treatment and is flanged.
- In the pipeline system and device of low temperature medium, low temperature ball valve with valve cover should be selected.
- On the pipeline system of the catalytic cracking unit of the oil refining unit, the lifting rod type ball valve can be selected.
- In the device and pipeline system of corrosive medium such as acid and alkali in chemical system, all stainless steel ball valve made of austenitic stainless steel and PTFE as valve seat sealing ring should be selected.
- Metal-to-metal sealing ball valves can be used in pipeline systems or devices of high temperature medium in metallurgical systems, power systems, petrochemical plants, and urban heating systems.
- When flow regulation is required, a worm gear driven, pneumatic or electric regulating ball valve with V-shaped opening can be selected.